Definition

Noun: 1. Variability in chemical composition without variation in crystalline form: In chemistry, allomerism refers to the phenomenon where two or more substances have different chemical compositions but share the same crystalline structure.

Usage

• General Usage: The term is used specifically in the field of chemistry and mineralogy to describe compounds that are isomorphous (have the same crystal shape) but differ in their elemental makeup.
  • The study of allomerism helps geologists understand how different minerals can form in the same crystal habit.

Examples

• Noun:
  • The two minerals exhibit allomerism; one is a calcium carbonate and the other is a strontium carbonate, yet they crystallize in identical forms.
  • Allomerism is a key concept when analyzing solid solutions in mineral series.

Advanced Usage

• In Scientific Context: The concept is often discussed in relation to isomorphism and solid solution series.
  • The allomerism observed in the feldspar group is due to the substitution of sodium for calcium within the crystal lattice.

Variants and Related Words

• Allomeric (adj): Pertaining to or characterized by allomerism.
  • The allomeric relationship between the two samples was confirmed by X-ray diffraction.

Synonyms

• Isomorphism (in a specific, related sense, though isomorphism emphasizes the same form, while allomerism emphasizes the different composition within that form).
• Isomorphous replacement.

Antonyms

• Polymorphism: The phenomenon where a substance can exist in more than one crystalline form.

Noun

1. (chemistry) variability in chemical composition without variation in crystalline form